Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$19.67	5.838%	$20.8183	$20.82	$20.80	$20.80
Purchase #2	$249.73	7.527%	$268.5272	$268.53	$268.55	$268.50
Purchase #3	$108.51	5.167%	$114.1167	$114.12	$114.10	$114.10
Purchase #4	$65.37	10.229%	$72.0567	$72.06	$72.05	$72.10
Purchase #5	$184.98	5.408%	$194.9837	$194.98	$195.00	$195.00
Purchase #6	$178.61	7.692%	$192.3487	$192.35	$192.35	$192.30
Purchase #7	$135.46	3.588%	$140.3203	$140.32	$140.30	$140.30
7 purchase totals =	$942.33		$1,003.1716	$1,003.18	$1,003.15	$1,003.10